Brightness is to video asloudness
is to audio. Bright is good.
Correct brightness is better.Excessive
brightness distorts color and creates glare. A better television image is created by an accurate reproduction of the image's brightness. Luminance is its directional intensity. TV brightness or luminace is measured
in lumen, foot lamberts, and nits. The choice of measurement depends on
the display type and use.

Lumen
Thelumen
is to luminance as the decibel is to loudness. The peak lumen
is
a popular home theater measurement of brightness that measures a projected
centered test
pattern of
a white block filling 10% to
20% of the screen. The remainder of the screen is black.The peak lumen measurement is limited to a small angle of radiation.
Because of this limitation, the American
National Standards Institute
offers a more useful and stringent measurement, the ANSI lumen.The
ANSI
lumen specification averages several
measurements taken at different
positions on a projected screen. As a reference; a projector
that
produces
1200 peak lumen,
may only measure 200 ANSI lumen.
Foot Lambert
Home
theater projector/big screen enthusiasts are more concerned about the level of light
reflected back towards the viewer
than the brightness of a projector. Projector brightness is important. But the
brightness of the reflected light decreases
as screen
square footage increases. It also decreases as the distance between the projector and screen increases. Therefore the ANSI lumen is not a sufficient unit of
measurement. The foot-Lambert
solves the problem. The foot-Lambert factors a projector's
brightness in ANSI lumen, the square
footage of the screen, the projector's distance from the screen, and
screen gain. It is the home theater standard of screen
brightness.
Asa reference,
theSociety
of Motion Picture and TelevisionEngineers
recommends
a level of 12 to 22 ft L with a goal of 16 ft-L
in a dark room. 16 foot-Lamberts is the reference of a
commercial cinema. If a low level of ambient light is
present and
unavoidable then 30 to 50 ft-L is the recommended goal.

Nit The
NIT is the measure of television or video monitor screen brightness. For
reference; NTSC TV
monitors were capable of about 100 Nits. New HDR capable
UltraHDTVs
are capable of about 4000 to 10,000 Nits.

It's A Matter of Scale
A better
television image is created by an accurate scale of brightness; a scale
that extends from the darkest black to brightest correct white.
This is described by the image's contrast ratio,
gray scale, and color temperature. Contrast
RatioContrast
ratio is an abused and often misunderstood television specification.
There are two types of contrast ratio measurement, dynamic and static, which has led
to even further misunderstanding.

DynamicDynamic
contrast
ratio is the most quoted by manufacturers, magazines, and retailers. It
refers to the deepest black versus the brightest white that a
television/monitor/projector & screen
can display; but not at the same time. It is an “all
off”
versus “all on” test. This simple test can generate impressive ratios such as 10,000:1,
20,000:1,
even higher.

A Contrasting Story
A friend of
mine shared the following story that put dynamic contrast into a real
world frame of reference.
He
was attending an Imaging Science
Foundation seminar. During the lecture, he observed that a
colleague of the lecturer had entered the rear of the room.
The
lecturer acknowledged his colleague with a nod as he continued to
speak until he finished his point.
The
lecturer then looked to his
colleague and asked, “How did you do?” His colleague
answered,
“300 to 1”. The lecturer responded, “No way!” His
colleague insisted, “300 to 1”.
Again the lecturer responded,
“No way"; then paused and then said, “Not
unless.......... you turned
off ....... the exit lights”. His colleague
admitted
with a grin, “Yes”.The
lecturer then turned to the
seminar audience to explain their exchange. His colleague had just
completed the calibration of a commercial digital theater projector.
300 to
1 referred to the contrast ratio he had achieved with the exit lights
off. The lecturer then said, “Given what you just heard, you
should be asking; where do contrast ratios exceeding 1000:1
come
from?” He
explained that
manufacturers often begin with the measurement of light in an
absolutely dark room. Well, there isn't any light. Its a dark
room. They
then turn on their projector with the lamp gain set at its highest
adjustment and measure the light at the projection screen.
The
difference is their contrast ratio specification. The seminar
audience responded with chorus of groans.

ANSI
Contrast Static Ratio
The American National Standards
Institute contrast ratio specification uses a standardized checkerboard
test pattern of black and
white rectangles. The ANSI standard simultaneously measures the difference between the
darkest black and brightest
white displayed side by side on a projected screen. That
is the source of the 300:1 number the ISF tech referred to.

GrayScaleThe
gray scale is a measurement of a
displays transition from black through gray to white.
It is the most
important TV attribute. This measurement is to video as frequency response is to audio. The gray scale measures the accuracy of
luminance which in turn determines the amplitude of the red,
green, and blue voltages.

Color
TemperatureHave
you ever heard
the
expression “red hot” or “white hot”? They have their origins
in black smithing and welding. As iron is heated
with
a
welding
torch; it changes in color from black to red, to white, to
blue.
This is the basis for the concept of color temperature
in degrees Kelvin.

C.I.E. Color This illustration is the International
Commission on Illumination official chart of visible color establish in 1930.
Envision the
illustration as a three dimensional cone. The X,Y points display the red,
green, blue color mix points. D65 (6500°
Kelvin) is gray scale amplitude Z point for the color white.
All color is
specified in terms of its temperature.
Higher temperatures >5,000°K
= cooler
(blue to white) color;
lower 2,700° – 3,000°K = warmer'
yellow thru red colors.

Color Space is the total specified space of human vision under the Color
Chart cone.

Color Gamut is the
color space allocated to a video specification such as HDTV.

Color Volume
measures color gamut as a percentage of the cone space specified.
For
example; UltraHDTV covers 75.8% of the total space. HDTV
covers
35.9% of the color space.

Bit Depth
or Color Depth
is the number of computer bits allocated to create a video color
sub-pixel. The number of bits determines the possible range
of
color shades.

For example; 8-Bit color
provides up
to 255 shades per red/green/blue sub-pixel for a total of 16.78 million
colors. 10-Bit color provides up to 1024 shades for a total
of
1.07 billion colors. 12-Bit color as employed by Dolby Vision provides
even more shades.

x.v.Color is the
color space specification for HDTV. It offers
a palate of color that nearly doubles the area of the original
NTSC color chart.